This invention relates particularly to a process for copolymerizing cis-1,3-pentadiene and trans-1,3-pentadiene to produce copolymers whose microstructure is uniquely and predominantly cis-1,4-polypentadiene.
Other conjugated diolefins, including 1,3-butadiene, isoprene, 2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene and 4-methyl-1,3-pentadiene also may be copolymerized with the cis-1,3-pentadiene isomer to prepare elastomeric copolymers.
The process utilizes a ternary catalyst system consisting of (A) a soluble chromium compound, (B) organometallic compounds such as a trihydrocarbylaluminum, and (C) a dihydrocarbyl hydrogen phosphite.
1,3-PENTADIENE MONOMER EXISTS IN TWO FORMS, NAMELY, AS THE CIS- AND THE TRANS- ISOMERS. Each monomeric unit when polymerized contains at least one asymmetric carbon atom. There theoretically are 11 possible stereo-regular polypentadienes.
Although at least eight different coordination catalyst systems based upon transition metals will polymerize trans-1,3-pentadiene, only two of them will polymerize cis-1,3-pentadiene.
U.S. Pat. No. 4,048,418 describes a process for polymerizing cis-1,3-pentadiene, using an iron catalyst system, to produce a polymer analyzing 93 percent cis-1,4-polypentadiene and which has a largely isotactic crystalline configuration; but the same iron catalyst polymerizes trans-1,3-pentadiene to a syndiotactic trans-1,2-polypentadiene. It is reported in Journ. Polym. Sci. 51, 463 (1961) that a vanadium catalyst polymerizes both the cis- and the trans-1,3-pentadienes to isotactic trans-1,4-polypentadiene.
U.S. Pat. No. 3,300,467 describes the polymerization of trans-1,3-pentadiene to polymers analyzing 65 to 87 percent cis-1,4-polypentadiene while using a titanium catalyst; and it is reported in Europ. Polym. Journ. 9, 189 (1973) that the titanium catalyst will isomerize the cis-1,3-pentadiene to trans-1,3-pentadiene and then polymerize the trans- monomer to a polymer containing 65 to 70 percent cis-1,4-polypentadiene.
U.S. Pat. Nos. 3,429,940 and 3,804,913 describe processes using a ternary catalyst comprising a chromium compound, triethylaluminum and an alkyl halide, which oligomerize conjugated diolefins such as isoprene or piperylene to form cyclic trimers such as trimethylcyclododecatriene. U.S. Pat. No. 3,754,043 describes a process that produces liquid polypentadiene while utilizing chromium acetylacetonate, a trialkylaluminum and a Schiff base as a catalyst system. Japenese Pat. No. 73 06,939 [see Chem. Abs. 80, 4644 n (1974)] describes a process for polymerizing 1,3-butadiene to a polymer in which 95 percent of the unsaturation is 1,2-polybutadiene, while utilizing a ternary catalyst consisting of a chromium compound, an organoaluminum compound and a phosphoric acid ester. Japanese Pat. No. 73 64,178 [Chem.Abs. 80, 109590v (1974)] reports the preparation of 1,2-polybutadiene by polymerizing butadiene in the presence of hydrogen using as catalysts chromium acetylacetonate, dibutylphosphonate and triisobutylaluminum.
Thus, there is no prior art concerning the copolymerization of cis- and trans-1,3-pentadienes to produce predominantly cis-1,4-polypentadienes, nor is there any art that teaches the copolymerization of any conjugated diolefins with cis-1,3-pentadiene to produce solid elastomers which contain a majority of polymer having cis-1,4-configuration.
A process has been found which will copolymerize linear and mono- branched conjugated diolefins containing from 4 to 8 carbon atoms.
A process and a catalyst system has now been discovered which makes it possible for the first time to copolymerize a mixture of cis-and trans-1,3-pentadiene isomers to predominantly cis-1,4-polypentadienes. Each of these cis-1,4 polypentadiene copolymers has a single relatively low glass transition temperature which makes these copolymers suitable for use in tire carcass compounds. It is now possible to copolymerize the cis-and trans-1,3-pentadiene isomers which normally occur together in certain fractions of byproduct C.sub.5 -hydrocarbon distillates from petroleum refining or petrochemical processes to form useful elastomeric products.
The previous processes for polymerizing mixtures of 1,3-pentadiene isomers have several disadvantages. For example, most of the prior art processes only polymerize the trans-isomer to produce polymers having less than satisfactory physical properties.